Content delivery network cache grouping

ABSTRACT

One or more content delivery networks (CDNs) that deliver content objects for others is disclosed. Content is propagated to edge servers through hosting and/or caching. End user computers are directed to an edge server for delivery of a requested content object by a universal resource indicator (URI). When a particular edge server does not have a copy of the content object from the URI, information is passed along a hierarchy (to a parent server, grandparent server, and, eventually, an origin server) until the content object is found. The origin server may be hosted in the CDN or at a content provider across the Internet. Once the content object is located in the hierarchical chain, the content object is passed back down the chain to the edge server for delivery. Optionally, the various servers in the chain may cache or host the content object as it is relayed.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a continuation patent application which claims priority fromU.S. patent application Ser. No. 12/732,942 filed on Mar. 26, 2010,which claims the benefit of U.S. Application No. 61/248,378 filed Oct.2, 2009. The entire disclosures of all these applications areincorporated by reference in their entirety for all purposes.

BACKGROUND

This disclosure relates in general to content delivery networks and, butnot by way of limitation, to serving content objects from edge servercaches of a content delivery network.

Content delivery networks (CDNs) are in the business of deliveringcontent for others. CDNs will either cache and/or host content for itscustomers. Efficiently delivering content for a large number ofcustomers creates difficulty. It would not be practical to store everypossible content object serviced by the CDN on every edge server. Oftencaches are used on the edge servers to store popular or importantcontent at the edges of the CDN. Popular content is less likely to havedelivery latency, while less popular content is more likely to take alonger time to locate and deliver.

In some cases, the content object is not available on the edge server.This situation is sometimes referred to as a cache miss. A universalresource locator (URL) provided to the CDN from a requestor is used tofind the content with a cache miss. The content may be hosted internalto the CDN or with a content provider. Finding the content object can betime intensive and affect the quality of service (QoS) perceived by therequestor. This is especially true for content that cannot be located inthe CDN and requires a request to an external origin server to find thecontent.

CDNs are typically comprised of a number of different locations thatserve content from, so called points of presence (POPs). In some cases,these different POPs are interconnected using the Internet and/orprivate backbones. Content not found in one POP may be readily availablefrom another POP. Even within a POP, there are typically a number ofdifferent edge servers that each fulfill requests for content. Thesedifferent edge servers have different capabilities and different contentin their cache. A cache miss at a particular edge server would beexpensive in QoS terms to fulfill from another server or even outsidethe CDN.

SUMMARY

In one embodiment, one or more content delivery networks (CDNs) delivercontent objects for others. Content is propagated to edge serversthrough hosting and/or caching. End user computers are directed to anedge server for delivery of a requested content object by a universalresource indicator (URI). When a particular edge server does not have acopy of the content object referenced in the URI, information is passedto another server, the ancestor or parent server to find the contentobject. There can be different parents servers designated for differentURIs. The parent server looks for the content object and if not found,will go to another server, the grandparent server, and so on up ahierarchy within the group. Eventually, the topmost server in thehierarchy goes to the origin server to find the content object. Theorigin server may be hosted in the CDN or at a content provider acrossthe Internet. Once the content object is located in the hierarchicalchain, the content object is passed back down the chain to the edgeserver for delivery. Optionally, the various servers in the chain maycache or host the content object as it is relayed.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating various embodiments, are intended for purposes ofillustration only and are not intended to necessarily limit the scope ofthe disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described in conjunction with the appendedfigures:

FIG. 1 depicts a block diagram of an embodiment of a contentdistribution system;

FIG. 2 depicts a block diagram of an embodiment of a content deliverynetwork (CDN);

FIG. 3 depicts a block diagram of an embodiment of a portion of acontent delivery network (CDN) that includes a server coupled to a CDNnetwork;

FIGS. 4A, 4B and 4C illustrate flowcharts of embodiments of a processfor finding a content object through various hierarchies; and

FIG. 5 depicts a block diagram of an embodiment of a lookup tree.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

The ensuing description provides preferred exemplary embodiment(s) only,and is not intended to limit the scope, applicability or configurationof the disclosure. Rather, the ensuing description of the preferredexemplary embodiment(s) will provide those skilled in the art with anenabling description for implementing a preferred exemplary embodiment.It being understood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope asset forth in the appended claims.

Referring first to FIG. 1, a block diagram of an embodiment of a contentdistribution system 100 is shown. The content originator 106 offloadsdelivery of the content objects to a content delivery network (CDN) 110in this embodiment. The content originator 106 produces and/ordistributes content objects and includes a content provider 108, acontent site 116, and an origin server 112. The CDN 110 can both cacheand/or host content in various embodiments for third parties to offloaddelivery and typically provide better quality of service (QoS) to abroad spectrum of end user systems 102 distributed worldwide.

In this embodiment, the content distribution system 100 locates thecontent objects (or portions thereof) and distributes the contentobjects to an end user system 102. The content objects are dynamicallycached within the CDN 110. A content object is any content file orcontent stream and could include, for example, video, pictures, data,audio, software, and/or text. The content object could be live, delayedor stored. Throughout the specification, references may be made to acontent object, content, content stream and/or content file, but it isto be understood that those terms could be used interchangeably whereverthey may appear.

Many content providers 108 use a CDN 110 to deliver the content objectsover the Internet 104 to end users 128. The CDN 110 includes a number ofpoints of presence (POPs) 120, which are geographically distributedthrough the content distribution system 100 to deliver content. Variousembodiments may have any number of POPs 120 within the CDN 110 that aregenerally distributed in various locations around the Internet 104 so asto be proximate to end user systems 102. Multiple POPs use the same IPaddress such that an Anycast routing scheme is used to find a POP likelyto be close to the end user in a network sense for each request. Inaddition to the Internet 104, a wide area network (WAN) and/or localarea network (LAN) 114 or other backbone may couple the POPs 120 witheach other and also couple the POPs 120 with other parts of the CDN 110.

When an end user 128 requests a web page through its respective end usersystem 102, the request for the web page is passed either directly orindirectly via the Internet 104 to the content originator 106. Thecontent originator 106 is the source or re-distributor of contentobjects. The content site 116 is an Internet web site accessible by theend user system 102. In one embodiment, the content site 116 could be aweb site where the content is viewable with a web browser. In otherembodiments, the content site 116 could be accessible with applicationsoftware other than a web browser. The content provider 108 directscontent requests to a CDN 110 after they are made or formulates thedelivery path by embedding the delivery path into the universal resourceindicators (URIs) for a web page. In any event, the request for contentis handed over to the CDN 110 in this embodiment by using an Anycast IPaddress corresponding to two or more POPs 120.

Once the request for a content object is passed to the CDN 110, therequest is associated with a particular POP 120 within the CDN 110 usingthe Anycast routing scheme. The particular POP 120 may retrieve theportion of the content object from the content provider 108.Alternatively, the content provider 108 may directly provide the contentobject to the CDN 110 and its associated POPs 120 through prepopulation,i.e., in advance of the first request. In this embodiment, the contentobjects are provided to the CDN 110 and stored in one or more CDNservers such that the portion of the requested content may be hostedfrom the CDN 110. The CDN servers include edge servers in each POP 120that actually serve end user requests. The origin server 112 holds acopy of each content object for the content originator 106.Periodically, the content of the origin server 112 may be reconciledwith the CDN 110 through a cache, hosting and/or pre-populationalgorithm. Some content providers could use an origin server within theCDN 110 to host the content and avoid the need to maintain a copy.

Once the content object is retrieved, the content object is storedwithin the particular POP 120 and is served from that POP to the enduser system 102. The end user system 102 receives the content object andprocesses it for use by the end user 128. The end user system 102 couldbe a personal computer, media player, handheld computer, Internetappliance, phone, IPTV set top, streaming radio or any other device thatreceives and plays content objects. In some embodiments, a number of theend user systems 102 could be networked together. Although thisembodiment only shows a single content originator 106 and a single CDN110, it is to be understood that there could be many of each in variousembodiments.

With reference to FIG. 2, a block diagram of an embodiment of a CDN 110is shown. Although only one POP 120 is shown in detail, there are anumber of POPs 120 similarly configured throughout the CDN 110. The POPscommunicate through a WAN/LAN 114 and/or the Internet 104 when locatingcontent objects. An interface to the Internet 104 to the POP 120 acceptsrequests for content objects from end user systems 102. The requestcomes from an Internet protocol (IP) address in the form of a URI.

Switch fabric 240 assigns the request to one of the edge servers 230according to a routing scheme such as round robin, load balancing, etc.In this embodiment, the switch fabric is aware of which edge servers 230have what capabilities and assigns within the group having thecapability to store and serve the particular content object referencedin the URI. A protocol such as cache array routing protocol (CARP) isused in this embodiment to disperse the URIs between the group of edgeservers 230. Every time that a particular URI is requested from thegroup, it is assigned to the same edge server 230 using CARP. The cachesgathered in a particular group as neighbors can be the other servers inthe current POP, less loaded servers in the current POP, servers havingthe capability to process the content object, a subset of serversassigned to a customer using the CDN to serve the content object, orsome other grouping of servers in the POP 120.

In another embodiment, the switch fabric 240 assigns the request to oneof the edge servers 230, which performs CARP to either service therequest or reassign it to a neighboring edge server 230. The switchfabric 240 sends each packet flow or request to an edge server 230listed in the configuration of the switch fabric 240. This embodimentdoes not have awareness of the particular capabilities of any edgeserver 230. The assignment can be performed by choosing the edge serverwith the least amount of connections or the fastest response time, butthe switch fabric in this embodiment assigns the packet flow somewhatarbitrarily using round robin or random methodologies. When the chosenedge server 230 receives the packet flow, an algorithm like CARP is usedby the chosen edge server 230 to potentially reassign the packet flowbetween a group of edge servers to the one dictated by the algorithm.For example, the switch fabric 240 could choose a second edge server230-2 being the next in the round robin rotation. The second edge server230-2 would perform CARP on the request and find that the first edgeserver 230-1 is being assigned this type of request. The request wouldbe reassigned to the first edge server 230-1 to fulfill.

In some cases, the CDN 110 is used to host content for others. Contentproviders 108 upload content to a CDN origin server 248. Although onlyone CDN origin server 248 is shown, it is to be understood that therecould be many spread among a number of locations. The content object canbe stored in the CDN origin server 248. The CDN origin server 248 servesthe content object within the CDN 110 to various edge servers 230 invarious POPs 120. After the content provider 108 places a content objecton the CDN origin server 248 it need not be hosted on the origin server112 redundantly.

Requests from end user systems 102 are assigned to an edge server 230that may cache the requested content object. On occasion, the edgeserver 230 receiving a request does not have the content object storedfor immediate serving. This so-called “cache miss” triggers a processwithin the CDN 110 to effectively find the content object (or portionthereof) while providing adequate QoS. The content may be found inneighboring edge servers in the same POP 120, in another POP 120, in aCDN origin server 248, or even an external origin server 112. Thevarious edge and origin servers 230, 248 are grouped for various URIsuniquely. In other words, one URI may look to one group of servers 230,248 on a cache miss while another URI will look to a different group ofservers 230, 248.

Referring first to FIG. 3, an embodiment of a portion 300 of a contentdelivery network (CDN) that includes an edge and/or origin server 304coupled to the WAN/LAN 114 is shown. The server could be an edge server,a host server or any other server that can supply content objects. Itmay be at the bottom of a hierarchy or a topmost position of thehierarchy within the CDN. Although this embodiment shows the server 304as operating as a cache, the content objects could be sticky within thecache such that the server 304 can also act as a host. Indeed, all thecontent on the server 304 maybe hosted in one embodiment.

Each server 304 in a CDN 110 can belong to any number of groups. Thegrouping defines where content in the universal resource indicators(URIs) will be searched when not found at a particular server 304. Whenthe server 304 cannot find a content object that is requested, it willgo to the WAN/LAN 114 or another network to find the content object solong as all options within the CDN are not exhausted. The URIs may ormay not belong to a group, but when they do, a particular ancestorserver will be handed the URI for fulfillment after a cache miss that ispotentially different from ancestor servers for other groups. At the topof any hierarchy of lookup tree, a server 304 experiencing a cache missmay go to the Internet rather than the WAN/LAN 114 to obtain a contentobject from an origin server of the content provider. The server 304includes a cache engine 316, a parent group map 324, and a cache 312.

The cache engine 316 receives the URI or request for content to fulfillthe request by serving the content object to the end user or server downthe lookup tree. The cache engine 316 checks the cache 312 for thecontent object. Where there is a cache miss, the cache engine 316 findsthe ancestor server to check for the content object. The cache engine316 receives the group variable that is derived from the original URI orcan derive a tree of ancestor caches from the URI itself.

In one embodiment, a universal resource indicator (URI) is requested andindicates a content object and optionally a group variable. In anotherembodiment, the group variable is not expressly within the URI, but theURI can be correlated to ancestor caches or groups using a lookup table.Optionally, the URI can also include a path, origin location,variable(s), a prefix, etc. In some form, the URI is passed to variousservers in an attempt to find a requested content object. It is to beunderstood that when the term URI is used, it doesn't necessarilyrequire any format and just conveys at least where to find a contentobject and the file or stream name. The URI either has the groupvariable or can be otherwise correlated to parent cache(s) or host. Forexample, ACME.llnw.net/videos/sports/game.mov?lex5 is a URI with an ACMEprefix, a llnw.net domain, a videos/sports path, a game.mov filename,and a lex5 group variable. The URI itself, the ACME prefix and/or lex5in this example could be used by servers to look-up where to look for acontent object when not found locally.

TABLE I URI Grouping Prefix Ancestor Server POP ACME.llnw.net San JoseSmith.llnw.net Dallas ShoeExpress.llnw.com Phoenix Vinex.llnw.com SanJose SDDT.llnw.com Denver

The URI grouping happens because each server is aware of its ancestorserver to use for each URI. The net effect of each server knowing theancestor server to refer to is to have a hierarchical tree that definesthe group. Table I is an example of grouping that could be stored in theparent group map 324. When a URI containing the ACME prefix is not foundin a server, the request is relayed to the San Jose POP 120 where it isassigned to another server for fulfillment.

Grouping can be used to provide different levels of QoS. Table II showssub-groups for a particular prefix that can be used to specify asub-group of servers within a POP 120. For example, the ACME customerdesignated with the ACME prefix in the URI may offer end user systems102 three possible levels of QoS. ACME could charge different rates forthe various levels of QoS. The Q1 URI variable would specify the fastestservers with the largest caches in the most favorable POP 120. The Q2variable would assign a lower caliber of server in the most favorablePOP 120. User systems 102 presenting the Q3 variable would be assigned aless favorable POP when the content object is not found.

TABLE II URI QoS Sub-Grouping Prefix Ancestor Server POP ACME . . . Q1?San Jose - Edge Group A ACME . . . Q2? San Jose - Edge Group B ACME . .. Q3? Denver

Each server looks to the variable from the URI to determine the nextancestor server up the hierarchy to query to when a content object isnot located locally. Where there is no ancestor cache for a URI, eachserver has a default hierarchy to find ancestor caches. There can be anynumber of possible servers up the hierarchy specified by any number ofURIs. In effect, the group variable or URI defines a tree that willspecify a flow that ultimately ends in an origin server or hostsomewhere. These trees can be selected differently for a number of URIsrather than relying on some default lookup tree.

The parent group map 324 stores at least one ancestor server locationfor each group variable or URI string. If there is no ancestor serverspecific to the particular group variable or URI, a default ancestorserver can be used. In any event, the parent group map 324 returnsancestor server locations or addresses to the cache engine 316. Forexample, a parent cache and grandparent cache would be returned for aparticular URI or group variable. Should the parent cache not respondfor whatever reason, the grandparent cache would be queried. The parentgroup map 324 can be a database or look-up table that is populated bythe CDN to implement a lookup tree.

The cache engine 316 requests the content object from the parent serveror grandparent server. Once the ancestor server responds, it will findthe content object locally or will look to its ancestor servers. Thiscycle can repeat many times through various levels in a hierarchy toultimately find the content object. The content object is relayed backdown the hierarchy to the cache engine 316 that places the contentobject in the cache 312 as the content object is passed to the end useror down the hierarchy.

Although this embodiment uses a chained approach to finding a serverwith the content object, other embodiments could use a star approach. Inthe star approach, the edge server receiving the URI would hold theentire lookup tree in its parent group map 324. The higher levels in thehierarchy could be successively queried for the content object. Thosequeries could be done overlapping in time to speed the lookup process.The content object is provided directly from the server higher in thehierarchy without involving every level in the hierarchy. The servers atvarious levels in the hierarchy could decide to store the content objector not in various embodiments.

With reference to FIG. 4A, a flowchart of an embodiment of a process400-1 for finding a content object through various hierarchies is shown.On a URI-by-URI basis, the lookup tree can change. The depicted portionof the process begins in block 404 where the edge server receives a URI.The URI indicates an address that was used to find the edge server, agroup variable and information to find the content object along withother information. Initially, the edge server checks its cache 312 forthe content object.

In block 412, it is determined if the content object is available in theedge server 412. We will cover the scenario where it is not foundinitially by progressing to block 420. The group variable is obtainedfrom the URI or it might be passed by a prior server lower in thehierarchy. The ancestor server is determined by referencing the parentgroup map 324 in block 424 with the group variable value. Although notshown, one or more back-up ancestor servers could be queried if theancestor server does not respond. In block 428, the content object isrequested from the ancestor server determined in block 424. Next,processing loops back to block 408 to see if the next higher server inthe lookup tree has the content object. These iterations continue untilthe content object is found in block 412.

Should the content object be found in the present iteration or in thehigher levels in the hierarchy of the lookup tree in block 412,processing continues to block 432. In the simple case, the edge serverhas the content object already before ever going through the loop. Wherethat is not the case, the content object is relayed down through thehierarchy from the server that had the content object to the edge serverin block 432. Each server in that chain may cache or otherwise store thecontent object. In block 436, the edge server that originally receivedthe request for the content object serves the content object through astream or download to an end user.

With reference to FIG. 4B, a flowchart of another embodiment of aprocess 400-2 for finding a content object through various hierarchiesis shown. The depicted portion of the process 400-2 begins in block 402where a URI request is received an edge server at the POP that specifiesa content object. The URI is rewritten in block 406. There may be manydifferent versions of a URI that correspond to a single content object.A look-up table is used to match as much of the URI as possible to anauthoritative name or source URL. The caches store content objects basedupon the source URL, which points to an origin server that can be usedto retrieve a content object not in the CDN.

It is determined in block 408 if the edge server receiving the requesthas the content object available locally. In block 412, a determinationis made if the content object is available and processing continues toblock 432 and 436 if the content object is within the edge server cachein the same manner as the embodiment of FIG. 4A.

Should the content object not be in the cache of the edge server asdetermined in block 412, processing continues to block 416. During therewrite process of block 406, many parameters such as the ancestorcache(s) are retrieved for the source URL and retrieved for use in block416. The ancestor cache(s) is the start of a potentially iterativeprocess that defines the tree of the cache group. In block 422, ancestorcaches are found using the parameters associated with the source URL. Aseach source URLs could have different ancestor caches, different cachegroups form on a URI-by-URI basis. The cache group is a function of thePOP receiving the request and ancestor cache preferences for each sourceURI.

The ancestor cache for a particular URI may be chosen for any number ofreasons. Which ancestors are used may adjust on a server, POP-wide orCDN-wide basis with periodic (e.g., hourly, daily, weekly, monthly, orsome other period) or real-time updates that react to health and loadingof particular servers and POPs. An ancestor may be chosen based uponwhether the content is hosted and/or cached in the CDN, the capabilityof a server to stream or process different content objects withdifferent media types, loading of a server, a server going down, aserver having health problems, loading of network connections of aserver, or other issues that would affect the suitability of aparticular ancestor server temporarily or permanently. For example, adata connection between a cache and an ancestor cache may be overloadedand the ancestor cache would change to one that was suitable.

A table or database stores ancestor cache information for each sourceURL or group of source URLs. Typically, there is a primary ancestor andat least one back-up should the primary not respond for whatever reason.In block 428, the source URI is requested of the primary ancestor cacheand any back-up ancestor caches, if necessary. Processing then loopsback to block 408 to repeat block 412, 416, 422, and 428 in a loop towork through the hierarchy. Although not shown, the highest level in thehierarchy would refer to the origin server to retrieve the contentobject.

With reference to FIG. 4C, a flowchart of another embodiment of aprocess 400-3 for finding a content object through various hierarchiesis shown. This embodiment is similar to the embodiment of FIG. 4B, butadds a block 414 between blocks 412 and 416. In block 414, neighboringservers are searched for the content object before resorting to anancestor cache out side those neighbors. The neighboring servers couldbe a group of the entire POP 120 or a sub-group of the servers withinthe POP 120. The serving of the content object may be reassigned to theserver holding the content object or may be relayed or proxied to theserver currently assigned to serve the content in various embodiments.

Referring to FIG. 5, a block diagram of an embodiment of a lookup tree500 is shown. This lookup tree 500 is simplified as there could behundreds or thousands of blocks on the lookup tree for a CDN.Embodiments could have different lookup trees 500 for differentcustomers, content formats, digital rights management, delivery methods,end user Internet service providers, bitrates, loading levels, etc. Thisembodiment shows three levels of hierarchy within the CDN 520 prior torequesting a content object an external origin server 516. By loadingthe parent group maps 324 for all the servers in the lookup tree 500will organize the hierarchy for a particular group variable.

In the first level of the hierarchy for the lookup tree 500, there arefive edge servers 504 that cache content objects. The edge servers 504could be distributed around the Internet in different ways. For example,edge cache A and B 504-1, 504-2 could be in the same POP or in differentPOPs. When a request goes edge cache A 504-1 and cannot be fulfilledinternally, edge cache B 504-2 is checked next for the content object.Should the content object not be found in edge cache B 504-2, therequest would go to another POP in Los Angeles 508-1. One or all thecaches in the Los Angeles POP 508-1 would be queried for the contentobject.

Should the Los Angeles POP 508-1 not have the content object, it wouldquery the POP having the San Jose POP 512. If not found in the San JosePOP 512, a server of the San Jose POP 512 would go back to the originserver 516 to retrieve the content object. In another embodiment, theCDN 520 hosts the content objects to serve as the origin server 516.

In another example, the content object request starts with edge cache D504-4. If not found there, a request would be made by edge cache D 504-4to edge cache C 504-3, but not to edge cache E. For example, edge cacheE may be in a different location or not suited to store and serve thecontent object. Should the content object not be found in edge cache C,the Denver POP 508-8 would be queried by edge cache C. If not found, thenext request goes from the Denver POP 508-8 to the San Jose POP 512.Finally, the origin server 516 would be queried if the content object isnot found in the San Jose POP 512.

In some cases, the search for a server with the content object can getcaught in a loop. A misconfiguration in the parent group maps 324 couldcause this problem perhaps as a update to the lookup tree 500 ispartially rolled out. When a server receives a request for the contentobject from another server, the server checks to see if in the chain ofservers relaying the request the receiving server is already listed.This would indicate a loop had developed. The loop could be broken byreferring the request to another POP or even to the origin server, forexample.

Specific details are given in the above description to provide athorough understanding of the embodiments. However, it is understoodthat the embodiments may be practiced without these specific details.For example, circuits may be shown in block diagrams in order not toobscure the embodiments in unnecessary detail. In other instances,well-known circuits, processes, algorithms, structures, and techniquesmay be shown without unnecessary detail in order to avoid obscuring theembodiments.

Also, it is noted that the embodiments may be described as a processwhich is depicted as a flowchart, a flow diagram, a data flow diagram, astructure diagram, or a block diagram. Although a flowchart may describethe operations as a sequential process, many of the operations can beperformed in parallel or concurrently. In addition, the order of theoperations may be re-arranged. A process is terminated when itsoperations are completed, but could have additional steps not includedin the figure. A process may correspond to a method, a function, aprocedure, a subroutine, a subprogram, etc. When a process correspondsto a function, its termination corresponds to a return of the functionto the calling function or the main function.

Furthermore, embodiments may be implemented by hardware, software,scripting languages, firmware, middleware, microcode, hardwaredescription languages, and/or any combination thereof. When implementedin software, firmware, middleware, scripting language, and/or microcode,the program code or code segments to perform the necessary tasks may bestored in a machine readable medium such as a storage medium. A codesegment or machine-executable instruction may represent a procedure, afunction, a subprogram, a program, a routine, a subroutine, a module, asoftware package, a script, a class, or any combination of instructions,data structures, and/or program statements. A code segment may becoupled to another code segment or a hardware circuit by passing and/orreceiving information, data, arguments, parameters, and/or memorycontents. Information, arguments, parameters, data, etc. may be passed,forwarded, or transmitted via any suitable means including memorysharing, message passing, token passing, network transmission, etc.

While the principles of the disclosure have been described above inconnection with specific apparatuses and methods, it is to be clearlyunderstood that this description is made only by way of example and notas limitation on the scope of the disclosure.

1. A method to cache content objects in a content delivery network (CDN)according to an arrangement of using different parent caches fordifferent URIs, the method comprising: receiving a first universalresource indicator (URI) at a cache of an edge server in a first pointsof presence (POP), wherein the first URI specifies a first contentobject; determining that the cache does not hold the first contentobject; analyzing the first URI to determine a first hierarchical treeof caches, the first hierarchical tree of caches having a plurality oflevels of caches to successively receive content-object requests uponcache misses at previous levels, the first hierarchical tree of cachescomprising the first parent cache; requesting the first content objectfrom the first parent cache in a second POP; receiving a second URI atthe cache of the edge server in the first POP, wherein the second URIspecifies a second content object; determining that the cache does nothold the second content object; analyzing the second URI to determine asecond hierarchical tree of caches, the second hierarchical tree ofcaches having a plurality of levels of caches to successively receivecontent-object requests upon cache misses at previous levels, the secondhierarchical tree of caches comprising the second parent cache differentfrom the first parent cache, wherein the second parent cache is in thefirst POP; and requesting the content object from the second parentcache.
 2. The method to cache content objects in the CDN according tothe arrangement of using different parent caches for different URIs asrecited in claim 1, wherein the first URI is from a first request forthe first content object, further comprising: analyzing the firstrequest to determine if the cache has received the first request from aloop, determining a third parent cache different from the first parentcache, and requesting the first content object from the third parentcache should the loop be determined.
 3. The method to cache contentobjects in the CDN according to the arrangement of using differentparent caches for different URIs as recited in claim 1, furthercomprising: analyzing the first URI; and choosing the first hierarchicaltree of caches from a plurality of hierarchical tree of caches basedupon the analysis of the first URI.
 4. The method to cache contentobjects in the CDN according to the arrangement of using differentparent caches for different URIs as recited in claim 1, furthercomprising: determining that the first parent cache does not hold thefirst content object; determining a first grandparent cache from theURI, the first grandparent cache being in the first hierarchical tree ofcaches; and requesting the first content object from the firstgrandparent cache.
 5. The method to cache content objects in the CDNaccording to the arrangement of using different parent caches fordifferent URIs as recited in claim 4, further comprising: determiningthat the second parent cache does not hold the second content object;determining a second grandparent cache from the URI, the secondgrandparent cache being in the second hierarchical tree of caches; andrequesting the second content object from the second grandparent cache.6. The method to cache content objects in the CDN according to thearrangement of using different parent caches for different URIs asrecited in claim 1, wherein: the analysis of the first URI comprisesidentifying a first level of quality of service, and the analysis of thesecond URI comprises identifying a second level of quality of service,the second and first levels being different.
 7. The method to cachecontent objects in the CDN according to the arrangement of usingdifferent parent caches for different URIs as recited in claim 1,wherein the first URI and the second URI include informationcorresponding to a level of quality of service, and wherein the firstand second POPs are associated with different levels of quality ofservice.
 8. A CDN for caching content objects according to a selectablearrangement of separate caches, the CDN comprising: a plurality of POPs;a plurality of edge servers distributed among the plurality of POPs,wherein the plurality of edge servers comprise a plurality of caches;and a cache parent determining function that receives a plurality ofURIs specifying a plurality of content objects for delivery to end usercomputers, wherein: the plurality of URIs include information thatallows selecting from the plurality of caches that would serve as aparent cache to find the content object should a cache, previouslyassigned the content object, not have the content object, and differentURIs have different parent caches, wherein: the plurality of URIsinclude a first URI and a second URI; both the first URI and second URIare received at a same POP; the first URI has a first hierarchical treeof caches in multiple POPs; the second URI has a second hierarchicaltrees of caches in multiple POPs; and the first hierarchical tree isdifferent from the second hierarchical tree.
 9. The CDN for cachingcontent objects according to the selectable arrangement of separatecaches as recited in claim 8, wherein the parent cache is changed toanother parent cache based upon loading of the parent cache.
 10. The CDNfor caching content objects according to the selectable arrangement ofseparate caches as recited in claim 8, wherein the plurality of POPs arelocated in a plurality of different geographic locations.
 11. The CDNfor caching content objects according to the selectable arrangement ofseparate caches as recited in claim 8, wherein the first URI and secondURI correspond to different content objects.
 12. The CDN for cachingcontent objects according to the selectable arrangement of separatecaches as recited in claim 8, wherein the URI is a portion of a URI. 13.The CDN for caching content objects according to the selectablearrangement of separate caches as recited in claim 8, wherein contentobjects can each be specified as sticky or ephemeral in the plurality ofcaches to optionally host or cache content objects.
 14. The CDN forcaching content objects according to the selectable arrangement ofseparate caches as recited in claim 8, wherein: according to the firsthierarchical tree, a cache in a second POP is ranked above a cache inthe same POP at which the first URI and second URI are received, andaccording to the second hierarchical tree, the cache in a first POP isnot ranked above the cache in the same POP at which the first URI andsecond URI are received.
 15. A method for caching content objectsaccording to a selectable arrangement of separate caches of a CDN, themethod comprising: receiving a first URI at a cache of an edge server ina first POP, wherein the first URI specifies a first content object;determining that the cache does not hold the first content object;analyzing the first URI to determine a first hierarchical tree ofcaches, the first hierarchical tree of caches having a plurality oflevels of caches to successively receive content-object requests uponcache misses at previous levels, the first hierarchical tree of cachescomprising the first parent cache; requesting the first content objectfrom the first parent cache in a second POP; receiving a second URI atthe cache of the edge server in the first POP, wherein the second URIspecifies a second content object; determining that the cache does nothold the second content object; analyzing the second URI to determine asecond hierarchical tree of caches, the second hierarchical tree ofcaches having a plurality of levels of caches to successively receivecontent-object requests upon cache misses at previous levels, the secondhierarchical tree of caches comprising the second parent cache differentfrom the first parent cache, wherein the second parent cache is in thefirst POP; and requesting the content object from the second parentcache.
 16. The method for caching content objects according to theselectable arrangement of separate caches as recited in claim 15,wherein the first URI is from a first request for the first contentobject, further comprising: analyzing the first request to determine ifthe cache has received the first request from a loop, determining athird parent cache different from the first parent cache, and requestingthe first content object from the third parent cache should the loop bedetermined.
 17. The method for caching content objects according to theselectable arrangement of separate caches as recited in claim 15,further comprising: analyzing the first URI; and choosing the firsthierarchical tree of caches from a plurality of hierarchical trees ofcaches based upon the analysis of the first URI.
 18. The method forcaching content objects according to the selectable arrangement ofseparate caches as recited in claim 15, further comprising: determiningthat the first parent cache does not hold the first content object;determining a first grandparent cache from the URI, the firstgrandparent cache being in the first hierarchical tree of caches; andrequesting the first content object from the first grandparent cache.19. The method for caching content objects according to the selectablearrangement of separate caches as recited in claim 18, furthercomprising: determining that the second parent cache does not hold thesecond content object; determining a second grandparent cache from theURI, the second grandparent cache being in the second hierarchical treeof caches; and requesting the second content object from the secondgrandparent cache.
 20. The method for caching content objects accordingto the selectable arrangement of separate caches as recited in claim 15,wherein: the analysis of the first URI comprises identifying a firstlevel of quality of service, and the analysis of the second URIcomprises identifying a second level of quality of service, the secondand first levels being different.